Thank you for writing. You are absolutely right to be concerned. What you are describing is not normal teenage angst. Your family is not making the problem “bigger than it is.” It is already far too big. I’m sorry your doctor wasn’t helpful, but not all medical doctors have the training or experience to deal effectively with what is clearly a mental health issue.
I strongly urge you and your family to seek out a licensed family counselor even if, especially if, your brother refuses to go. People don’t need to have a mental health issue themselves to see a therapist. Often our job as therapists is to help a family figure out how to get their loved one the help they need. A counselor who knows local resources can offer your family both practical help and support as you deal with your brother.
I can’t make a diagnosis on the basis of a letter alone. However, I can say that your brother’s behavior is consistent with a diagnosis of depression. He may have retreated into the world of the laptop and games because he feels he is safer there. He also may feel (and be) more competent in the company of other gamers on the Net than in real life, face to face, interactions with peers. Gamers only care about how someone plays the game. Peers judge each other on their appearance and social skills. Your brother avoids all judgment by focusing only on his laptop.
He has also become quite entitled. He is essentially making you all responsible for his health and well-being. In order to get you all to let him avoid life, he is manipulating you with his anger and blackmailing the whole family with his treats of suicide and homicide. I know it can be terrifying, especially if he is saying things like “you’ll be sorry”. This, again, is material for a local therapist to assess with you. The therapist will make recommendations for how to deal with his threats as well as for how to engage him in treatment.
I wish you well.